Bluelab pH Pen - Temperature Compensated Digital pH TesterBluelab pH Pen Temperature Compensated Digital pH Tester The Bluelab pH Pen is a great little hand held device for measuring the acidity alkalinity of your nutrient solution. Bluelab products are trusted by growers across the globe for their accuracy and reliability the handy new pH Pen is no exception! With temperature compensation, it provides highly accurate readings, as well as displaying the temperature of your nutrient solution onscreen. How the